The Sagebrush Cooperative

NW High Desert: Sagebrush Steppe Wildlife Species

The sagebrush steppe provides unique habitat that is used by 90 bird species and more than 85 mammals for forage, shelter, nesting and breeding sites. Many wildlife species are dependent on this habitat and cannot survive without sagebrush and its associated forbs and grasses. Pygmy rabbits, sage-grouse and sage thrashers represent species which are declining in concordance with shrinking and degraded sagebrush steppe habitat.

Greater sage-grouse

Greater sage-grouse (Centrocercus urophasianus) are wide ranging sagebrush obligates requiring large areas with a variety of sagebrush communities to meet life-history needs: Lekking habitat (areas used for communal breeding displays) often contains little to no shrub cover, a strong perennial grass component is needed for nesting habitat, forb rich communities are needed for brood rearing, and relatively dense stands of sagebrush are required during winter months.

Greater sage-grouse were once found in most sagebrush (Artemisia spp.) habitats east of the Cascades in Oregon. Today, greater sage-grouse distribution has decreased by 50% of its former range (Schroeder et al. 2004). Conservation assessments suggest that habitat loss, cheatgrass invasion, disease, predation, herbicides, and drought could be factors in greater sage-grouse population declines. However, habitat degradation and fragmentation are considered the leading causes of population decline. The majority of past habitat loss occurred in the Columbia Basin during the late 1800s and early 1900s as a direct result of sagebrush conversion to agricultural land. Remaining sage-grouse populations have fluctuated markedly since the mid 1900s with notable declines in populations from the 1950s to early 1970s. In the last 20-30 years the current range has continued to be diminished by fire, juniper encroachment, and other conversions. Population declines during the latter part of the 1900s have led to considerable concern for the species and subsequent conservation planning in all western states where it occurs. The U.S. Fish and Wildlife Service (USFWS) received three petitions to list the greater sage-grouse range-wide as endangered or threatened, and began a formal status review in April 2004. In 2005, USFW determined that actions to protect sage-grouse range-wide were not warranted under the Endangered Species Act. In December 2007, the district court ruled that USFWS must now wait for the next major sage-grouse scientific assessment and make a new listing determination by February 2010.

Despite the negative pressure on sage-grouse habitat, some sagebrush rangelands have persisted, particularly in southeast Oregon and adjacent areas of Idaho, California and Nevada. Much of the sage-grouse habitat in the Sagebrush Cooperative area comprises contiguous habitat with minimal threats of oil, gas, or coal-bed methane development. However, there is potential and interest to develop wind-energy grids in important sage-grouse regions. Protecting large expanses of sagebrush communities from fragmentation and habitat degradation should ensure sustainable populations into the future. Concentrating on the habitat needs of sage-grouse will focus on maintenance and enhancement of sagebrush habitats, which are important to a number of other wildlife species (Maser et al. 1984). Because sagebrush habitat within the Sagebrush Cooperative is a stronghold for this species, conservation actions here are critical to the future success of this species.

Other sagebrush associated avian species

The decline of the sage-grouse in the Northwest shrub-steppe landscape is perhaps the most publicized issue related to habitat degradation and decline among sagebrush-associated species. However, many other important avian species are dependent on sagebrush and its attributes for survival. Despite the uniform appearance of large expanses of sagebrush steppe, there exists much diversity within this habitat that is essential to the survival of the many species of birds that inhabit this landscape. While many species depend on sagebrush, they may differentially utilize it as shelter, forage, breeding sites, nesting sites or other purposes. Birds also differ in their preferences for specific plant associations, patch size, shrub density, vertical structure, understory composition and various other attributes.

The populations of many of the avian species found within these habitats are generally thought to be declining (Dobkin and Sauder 2004). Much of the population trend data for these shrub steppe species is obtained through annual Breeding Bird Surveys (BBS). Although these surveys can provide important information regarding the status of these species, some areas within sage steppe habitat are among the least consistently sampled of all areas covered by the BBS (Dobkin and Sauder 2004). The BBS routes that do exist in this region under-represent sagebrush habitats and some of the species are considered poorly detected by BBS methodology (Dobkin and Sauder 2004). As a result, the specific status of many of these populations in the NW High Desert remains unknown or disputed.

As management practices and restoration practices are refined to protect sage-grouse, it is important to understand the diversity of habitats within sage steppe ecosystems that are in need of conservation to properly protect a wide variety of avian species. The following species accounts detail the ecology of several avian species affected by human utilization and degradation of sagebrush steppe and whose requirements can help shape appropriate sagebrush-steppe management.

Black-throated sparrow (Amphispiza bilineata): These naturally rare sparrows are found in arid sagebrush deserts, shrublands and sparsely vegetated desert scrub. They require desert scrub habitats with sparse shrubs (below 25 percent vegetative cover) and water sources during dry seasons (Johnson et al. 2002). They nest on or very close to the ground and may be sensitive to ground disturbances such as human traffic, off-road vehicles, or trampling by livestock (Paige and Ritter 1998, USDA Forest Service 1994).

Brewer’s sparrow (Spizella breweri): Brewer’s sparrows are often the most abundant bird species in appropriate sagebrush habitats. This species is a shrub obligate that is threatened by large scale reduction and fragmentation of sagebrush habitats. They are positively correlated with high sagebrush vigor, shrub cover, above-average vegetation height, bare ground, and horizontal habitat heterogeneity (patchiness) and negatively correlated with grass cover, spiny hopsage, and budsage (Knopf et al. 1990, Larson and Bock 1984; Rotenberry and Wiens 1980; Wiens 1985; Wiens and Rotenberry 1981).

Lark sparrow (Chondestes grammacus): Lark sparrows generally prefer structurally open habitats with scattered shrubs or trees and are associated with shrubland ecotones and edges (Martin and Parrish 2000). The tendency of this species to occupy disturbed sites and edges between two habitat types has helped their numbers remain stable throughout the West. In sagebrush steppe habitat, lark sparrows avoid burned areas devoid of woody vegetation, preferring instead areas dominated by big sagebrush (Artemisia tridentata) within unburned sites (Bock and Bock 1987). Appropriate management includes providing suitable habitat (open grasslands with sparse to moderate herbaceous and litter cover, and a shrub component) and possibly allowing moderate grazing (Martin and Parrish 2000).

Loggerhead shrike (Lanius ludovicianus): Shrikes utilize juniper and sagebrush steppe with tall shrubs and openings. In northeastern California sagebrush steppe, loggerhead shrikes are most common in Wyoming sagebrush (Artemisia tridentata ssp. wyomingensis) and Basin big sagebrush (A. t. ssp. tridentata) communities, and are less frequently encountered at higher elevations in mountain sagebrush (A. t. ssp. vaseyana; Humple et al. 2002). Densities are also high in this region in greasewood (Sarcobates vermiculatus) communities (Shuford and Gardali 2008). In the NW High Desert, this species hunts from tall shrub perches and nests in sagebrush and other sagebrush steppe shrub species. Nest survivorship has been found to be lower following fire (Humple and Holmes 2006, Woods and Cade 1996). Further degradation and loss of sage steppe habitat would likely negatively affect this species.

Sage thrasher (Oreoscoptes montanus): Sage thrashers exhibit strong site fidelity and will return to nesting sites even after habitat alteration that could negatively affect productivity (Knick and Rotenberry 2002; Wiens and Rotenberry 1985). There is a high probability of sustaining thrashers wherever native sagebrush habitats are maintained with high shrub vigor, tall shrubs, horizontal shrub patchiness, and an open understory of bare ground and native bunchgrasses and forbs (Petersen and Best 1991, Rotenberry and Wiens 1980).

Sage sparrow (Amphispiza belli): This sage obligate sparrow is found in large contiguous patches of sagebrush covered valleys and high plateaus of eastern Oregon and are strongly associated with sagebrush for breeding (Martin and Carlson 1998; Paige and Ritter 1998; Reynolds 1981). Their presence is positively correlated with big sagebrush (Artemisia tridentata), shrub cover, bare ground, above-average shrub height, and horizontal patchiness and negatively correlated with grass cover (Rotenberry and Wiens 1980; Wiens and Rotenberry 1981; Larson and Bock 1984).

Game species: Pronghorn antelope, mule deer, elk and bighorn sheep

Sagebrush has been demonstrated to be a critical food source for several games species during various seasons of the year. Big sagebrush is a highly nutritious and digestible food source for big game animals. During winter, big sagebrush has a higher crude protein level and digestibility than most other shrubs or grasses. Shrubs (primarily sagebrush) are used almost exclusively by pronghorn from November through March and moderately through the other months (WGFD 2009). Pronghorn antelope (Antilocapra americana) prefer short growing sagebrush, presumably because their keen eyesight is adapted for detecting danger at long distances (McAdoo et al. 2003).

Mule deer (Odocoileus hemionus) are closely associated with sagebrush-grass communities in much of their range. Being primarily shrub eaters (browsers), vegetation changes favoring shrubs often benefit mule deer populations. Many forbs and shrubs associated with sagebrush communities are important in mule deer diets, with grasses used primarily in spring (McAdoo et al. 2003). Forb use is highest in summer, and on many mule deer ranges, big sagebrush is the staple component in winter and early spring with the “Wyoming” subspecies being preferred (Kufeld et al. 1973). Elk (Cervus canadensis) generally depend upon grasses for forage throughout much of their range, but they also eat shrubs, including big sagebrush, especially during fall and winter (Kufeld 1973). In parts of the Great Basin, elk use sagebrush-dominated habitats in other seasons as well. Bighorn sheep (Ovis canadensis) also use sagebrush-grass communities in some areas, especially as winter range. Although grasses are typically the major component in the bighorn sheep diet, shrubs are important, and big sagebrush is a preferred shrub (McQuivey 1978).

Sagebrush also provides cover (nesting, resting and escape) for a wide variety of game and non-game species (e.g. protective cover for fawns, calves). Additionally, the thick canopy of sagebrush protects valuable understory vegetation from livestock grazing. The crowns of sagebrush plants also tend to breakup and weaken hard crusted snow on winter ranges making it easier for big game to access understory plants for foraging (WGFD 2009).

Pygmy rabbit

The pygmy rabbit (Brachylagus idahoensis) is the smallest rabbit species in North America. Historically, pygmy rabbits were found throughout the sagebrush steppe biome of the Great Basin and adjacent intermountain regions of the western United States, including portions of Oregon, California, Nevada, Utah, Idaho, Montana, Wyoming, and Washington (USFW 2007). Pygmy rabbits are typically found in habitat types that include tall, dense stands of sagebrush (Artemesia spp.), on which they are highly dependent for both food and shelter throughout the year (Larrucea and Brussard 2008, USFWS 2007). Sagebrush comprises 99% of their winter diet (Gates and Eng 1994). The pygmy rabbit is one of only two rabbit species in North America that digs its own burrows and, therefore, is most often found in areas that also include relatively deep, loose soils that allow burrowing (Weis 1984).

The Columbia Basin pygmy rabbit is a distinct population segment that inhabits a geographic area extending from northern Oregon through central Washington (USFWS 2007). Columbia Basin pygmy rabbits and active burrows have declined dramatically over the past decade and the subspecies may be extinct in the wild. This population segment was federally listed as endangered in 2003 (USFWS 2007). Large-scale loss and fragmentation of native shrub-steppe habitats, primarily for agricultural development, likely played a primary role in the long-term decline of the Columbia Basin pygmy rabbit (USFW 2007). The added pressures of disease, livestock grazing, fire, mining, energy development, recreation, predation, intra- and inter-specific competition, natural stochastic events such as floods and drought, mortality caused by collisions with vehicles and genetic drift have further imperiled the future survival of this population segment (USFWS 2007). Captive breeding efforts, initiated in 2001, have met with limited success.

Pygmy rabbit populations outside of the Columbia Basin face many of the same threats that have lead to the unfortunate status of that distinct population segment. In 2008, a US Fish and Wildlife Service 90-day finding on a petition to list the entire population under the Endangered Species Act was found to present substantial information indicating that listing the pygmy rabbit may be warranted. The species status is currently under review.

Recovery strategies for this species include protection of existing habitat, identification and management of lands for creation of new habitat, monitoring of the pygmy rabbit population, and research to better understand the effects of management actions (WDFW 1995). To increase the extent of pygmy rabbit habitat, efforts should be directed at identifying lands where soil conditions are suitable for the species. Grazing, if it occurs in pygmy rabbit areas, should be managed to be compatible with the species needs and in all pygmy rabbit areas, steps should be taken to reduce the risk of range fire (WDFW 1995).